This invention relates to the field of transmitting/recording computer-generated displays over low bandwidth channels, e.g. audio channels, perhaps simultaneously with other audio-visual information on additional channels. More particularly, this invention proposes to convert computer-generated codes necessary to generate the displays into, for example, audio tones; to transmit/record those audio tones over an audio bandwidth channel simultaneously with other audio/video signals; to reconvert the audio tones back into computer codes from which a computer display can be generated by a local computer monitor; and to simultaneously generate the computer display, the video display, and the audio synchronously as they were recorded/transmitted. With this invention, instructional sessions or teleconferences which include computer display or output can be broadcast or videotaped, complete with all the computer-displayed information.
At present, researchers are seeking a satisfactory method by which a high-resolution, computer-generated display may be successfully transmitted/recorded as part of a televised class or teleconference. Part of the problem is the higher resolution typically associated with computer displays. For example, a color monitor for a computer typically operates at a 20 MHz rate. This compares to the 3.58 MHz rate of normal NTSC television. Thus, to transmit/record the high-resolution images, it is necessary to have a transmission channel with sufficient bandwidth to resolve them, i.e. 20 z. One known solution is to provide a dedicated transmission channel having very large bandwidth; but this is impractical and requires highly specialized equipment.
A modem may be used to convert computer-generated information into a series of encoded audio tones which are then transmitted over an audio channel (telephone line) to a second modem which reconverts the audio tones into the computer-generated information. However, this use of a modem is limited in that no other audio or video information may be transmitted simultaneously with the computer-generated information. In addition, audio tones output from a modem have never been recorded on a recording medium simultaneously with other audio and video information. Such shortcomings are a serious problem when the desired communication involves the transmission of computer-generated images together with audio and/or video signals. The problem is evident in computer-training classes. Such classes usually involve aural and visual presentations including a high-resolution computer display monitor, as well as the normal chalkboard/viewgraph and verbal instruction. Where it is desired to transmit and/or record such a computer training class, it has been found impossible to transmit/record the high resolution, computer-generated image together with the normal video and audio signals. When an attempt is made to transmit/record a video signal which contains an image of the professor together with an image of the computer monitor, it has been found that the computer-generated image cannot be properly displayed due to the different operating bandwidths of the video camera and the computer monitor.
Since the number of computer training classes is rapidly increasing and since the availability of such classes can be improved by providing remote locations at which the classes may be observed, there is a need to provide an apparatus and method by which the computer-generated, high-resolution image may be transmitted/recorded simultaneously with the audio and video signals.
Those having skill in this field recognize that one attempt to address this problem is Videotex. Videotex is a method by which existing communications media such as telephone, cable, and television may be utilized to interchange computerized mass information. Such Videotex systems may transmit computer-generated images. However, such images are typically displayed on a television which does not have the same resolution as a computer monitor. In addition, the known Videotex systems such as Bildschirntext, Dow Jones News/Retrieval, Grassroots, Indax, NAPLPS, Prestel, Teleguide, Teletel, Viewtron, along with similar ASCI-II-based systems such as Compu Serve, Dialog, etc. are incapable of transmitting computer-generated images together wth standard video and/or audio signals.
Therefore, there remains a need for a method and apparatus of transmitting high-resolution, computer-generated images simultaneously with video and audio signals.
It is usual to communicate with general-purpose computers by means of a computer terminal. This terminal is designed to provide an operator with a convenient means of passing information to the computer, e.g., a keyboard or a "mouse"; and to provide the computer with a convenient means of passing information to the operator, e.g., a CRT display. In some cases the thermal is physically separate, as in "mainframe" or "timesharing" systems; in other cases the terminal is an integral part of the computer itself, as in "personal" or "laptop" computers. In either of the cases, the system operates almost exclusively with binary-valued electrical signals which are construed as binary pieces of information--binary digits (bits). The meaning of a particular sequence of bits is defined in the computer by hardware, by "firmware", and by software.
For systems in which the computer is physically distinct from the terminal, binary information passes between the two according to some electrical transmission standard--either as "parallel" information--in which eight bits are transmitted simultaneously on eight wires, or as "serial" information--in which one bit at a time is transmitted along a single wire. An example of a serial transmission standard is the so-called RS-232 protocol. (The present invention's description will refer to the RS-232 protocol as the usual standard for transmitting computer information serially. However, the present invention is not restricted to that particular serial standard.)
The computer terminal is a "convenient" means by which an operator can communicate with a computer, because it allows that operator to press the key labeled "a" rather than enter a particular bit sequence; and to receive a geometric figure "a" on the CRT rather than receive just the bit sequence. The fact that a computer sends out a bit sequence it considers the letter "a", and the terminal displays an "a" when it receives that bit sequence, means that the computer and terminal have been designed around the same definition of bit patterns or sequences. Definitions include, but are not limited to, the so-called ASCII and EBCDIC standards for interpreting bit patterns as alphanumeric characters, and Tektronix-4010 standards for interpreting bit patterns as graphics instructions. For graphics, when a terminal is designed to interpret graphics instructions, it will generate a line on the CRT when it receives the appropriate bit sequence. (In the explanation of the present invention below, the bit patterns or sequences are referred to generically as "computer codes or display codes". Since the present invention does not depend on a particular definition of the bit patterns, only that the computer and the associated terminal interpret the patterns the same, the phrase "computer code" is a sufficient descriptor.)
The computer can be connected to the terminal in several ways: directly, whereby wire(s) capable of carrying the digital computer codes ink the two; or indirectly, whereby the computer codes are carried over additional communication media. The most typical indirect means is through telephone lines. But digital computer codes cannot be transmitted by most telephone lines; consequently, the codes that emanate from the computer (or terminal) first must be converted to an analog form compatible with the transmission characteristics of the telephone line, and then must be reconverted into the original digital from for reception by the terminal (or computer). This conversion-reconversion is effected by a pair of devices called modems (MOdulators-DEModulators), one at the computer end to convert the digital computer codes into telephone compatible signals, the second at the terminal end to reconvert the telephone signals into the digital computer codes. These same devices work in the opposite direction when information is passed from the terminal to the computer.
The particular technique by which modems convert the digital computer signals for transmission over non-computer communication lines is transparent to the computer user and need not be elaborated upon. The converted signals need only be compatible with the transmission medium. For example, the need to be converted to audio tones for transmission over telephone lines. The computer/terminal connections on the modem need be compatible with the digital signal protocol used by the computer and terminal, e.g. RS-232. The definition of the "computer codes" designed into both the computer and terminal is of no concern to the modem and the transmission of information. The modem converts/reconverts digital electrical signals without regard to their eventual interpretation by the computer/terminal.
It is with these computer-related elements that the present invention is concerned.